In the melting processes of metal and alloy, the change of chemical component is required to be detected, so as to control the product quality and judge a melting end. At present, due to the lack of an advanced and effective online measurement technology, the offline detection manner of manual sampling and sample preparation is generally adopted in the melting processes. For example, during the steel melting process, in the detection of high-temperature molten steel, the molten steel is required to be taken onto an analytical instrument for measurement and analysis after a series of processes of sampling, cooling, grinding, polishing, etc., and it needs to take 3 to 5 minutes in the entire process that will occupy more than one tenth of melting time. This time-consuming offline detection manner not only causes backward quality control, but also causes the waste of large amount of resources and energy resources. Moreover, detection equipment is expensive, bulky and difficult to adapt to modern melting production requirements.
A Laser Induced Breakdown Spectroscopy (LIBS) is a technology of using laser for exciting plasma and then using the emission spectra of the plasma for performing element detection and analysis. It does not need a complicated sample pretreatment process, has not strict requirements for the appearance and the size of samples, has low consumption quantity of the samples, is suitable for solid, liquid and gas simultaneously and can be used for performing simultaneous determination on multiple elements. Therefore, this technology presents an excellent application value in the aspects of in-situ, online, quick and remote analysis.
With the increasing enlargement, high speed and continuity of the production mode of metallurgical industry, there is an increasingly urgent demand for an in-situ online detection technology for liquid metal component, and an online detection device based on the Laser Induced Breakdown Spectroscopy (LIBS) begins to appear.
The literature (Reinhard Noll, Laser-Induced Breakdown Spectroscopy: Fundamentals and Applications, Springer 2012) presents the research status of detection equipment by using LIBS currently. Analytical equipment applied to metal component mainly includes short-distance laboratory equipment. The short-distance laboratory equipment is accurate in measurement and short in time required (tens of seconds), but has enormous volume and higher requirement for the environment, so it cannot better adapt to the online monitoring of complex environments, such as steel factory, etc.
The literature (Lin Xiaomei, Cao Jiqing, Yin Qinghui, and Liu Xiaoqing, Online Analysis of Silicone Content in AOD Furnace Based on LIBS, Magnesium Alloy, 2009 (1): 41-44) presents a device for detecting the content of Si element in an AOD furnace by using LIBS. The device uses a self-design sampler for sampling in the furnace. After that, component detection is performed in a sample pool of the device. The device has shorter detection distance and relatively complicated structural design, can only measure a single element and cannot simultaneously measure multiple elements.
The literature (G Mathy, B. Monfort, B. Vanderheyden, V. Tusset, Liquid steel process: advanced on line sensors under development at CRM. Metall. Anal. 30 (Suppl.1), 6-14 (2010)) presents a TeleLis system for realizing long-distance LIBS detection by using a Newtonian telescope system. The TeleLis system can realize the analysis of element component on a required measuring sample within the range of 3 to 12 meters. However, because a front optical path thereof is an open structure, an ambient environment and air will influence spectrum accuracy. Moreover, the character spectral lines of elements such as C, S, P, etc. are in an ultraviolet region. Air component in the open optical path absorbs these elements strongly, so these character elements cannot be measured.
The literature (Robert De Saro, Arel Weisberg, and Joe Craparo, In Situ, Real Time Measurement of Aluminum, Steel, and Glass Melt Chemistries Using Laser Induced Breakdown Spectroscopy, 2005 ACEEE Summer Study on Energy Efficiency in Industry 2005) reports a device for online measurement of elements such as Al, Cu, Fe, Mn, etc. in an aluminum alloy solution in industrial situ. A probe is inserted into a furnace body for directly measuring a metal solution surface. However, an optical structure is contained inside the probe of the device, and needs to be protected. The probe has a complicated structure.
The literature (Mohamed A. Khater, Laser-induced breakdown spectroscopy for light elements detection in steel: State of the art, Spectrochimica Acta Part B 81 (2013) 1-10) presents the monitoring situation of light elements by using LIBS in metal melting. Because the character spectra of the light elements mainly focus on an ultraviolet region and a deep ultraviolet region, the current major method is to generate an inert gas environment or a vacuum environment for performing measurement, while special gas environments of optical paths are relatively shorter and cannot better adapt to the severe environment of a factory.
In summary, there is currently no complete set of online monitoring equipment for simultaneous measurement of multiple elements (nonmetal elements such as C, S, P, etc.) based on LIBS capable of well adapting to the severe environment of a steel melting factory and having simple structure, strong applicability and lower manufacturing cost and maintenance cost. The existing equipment has different limits in the aspects of structural complexity, environmental need, measurable need, etc., and has relatively narrow application scope.